This invention relates to a permanent magnet generator apparatus and particularly to such a generator apparatus adapted for energizing of a voltage regulator of an regulated alternator system.
Permanent magnet generators have been available for many years. The generators are of an advantageous construction and may employ permanent magnets, limiting the necessity for a separate power supply for excitation of the generator. The advantage associated with permanent magnets has been significantly increased with the advance in the construction and availability of materials for permanent magnets. Various rare earth metals provide high strength permanent magnets having a long magnetic life. Permanent magnet generators have generally been more or less restricted to precision generators and particularly generators in which the mechanical and centrifugal forces on the magnets are not severe. Rare earth magnets are particularly brittle and particularly subject to mechanical damage. The holding means on the magnets, particularly where large forces are present, require careful mechanical construction. The constructional limitations have limited the use in certain applications.
For example, relatively large alternators which are driven by engines, turbines and other prime movers are widely used in industry to provide an alternating current power supply. Three-phase alternators providing voltages of 240/480 volts are commonly commercially marketed. Such alternators universally include a regulator for regulation of the voltage, current and/or frequency. The regulator requires a logic power supply.
The alternators are also provided with appropriate excitation from an exciter generator which is coupled to the common shaft with the alternator. The output of the exciter is rectified and coupled to the field winding of the alternator. The regulator and exciter may be powered through a feedback coupling to the output of the alternator. In many applications, a separate power supply is advantageously used for powering the voltage regulator and the exciter. Permanent magnet generators are adapted to such use and have been used commercially in such structures. In such construction, the permanent magnet rotor of the generator is conventionally mounted to the common shaft unit with the alternator field rotor and the exciter rotor winding. A stationary three phase output winding is connected through a suitable rectifying and signal processing circuit to provide the necessary power to the voltage regulator and to the exciter. The permanent magnet generator of a conventional construction is a reasonably large heavy device and has been mounted outboard of the exciter. In at least one instance, the alternator has been mounted inboard of the exciter, that is, between the exciter and the main alternator. The permanent magnet generators have generally applied relatively large permanent magnet members secured in side-by-side relation circumferentially about the rotor base, and with adjacent magnets oppositely polarized. A suitable mechanical keeper in the form of a heavy band is clamped about the magnets to hold the magnets in place. This construction is necessary because of the large centrifugal forces on the magnets and the requirement of establishing a stable and reliable high force support of the magnets.
Although such systems have been used in commercial devices and provide a satisfactory alternator operation with the general advantages provided by the separate power supply, the permanent magnet generator is relatively large and presents certain difficulties from the standpoint of suitable construction not only of the generator but the mounting of the generator within and as a part of the main alternator system. Although a permanent magnet generator using rare earth permanent magnets would appear to be advantageously used, the nature of such magnets and the large forces and environment in an alternator makes the use of such magnets difficult, and the present inventor knows of no such use.
There is a distinct need for a small, compact permanent magnet generator which can be applied to and integrated into an alternator unit. Such permanent magnet generator may of course also advantageously be applied to other applications.
The permanent magnet generator must be particularly adapted to an economic commercial implementation, generally requiring the use of mass production technology which is presently commercially available.